1. Field of the Invention
The present invention relates to modular jacks and, particularly, to a modular jack equipped with a foolproof mechanism for preventing insertion of a modular plug having a number of terminals that is not a predetermined number.
2. Description of the Related Art
Modular jacks and plugs for use in telephone equipment or local area network (LAN) are well known. There are six-pole or eight-pole type modular jacks and plugs according to the number of terminals installed. The arranging pitch of the terminals are the same for both the types so that a six-pole type modular plug can be plugged by mistake into an eight-pole type modular jack, causing an electrical malfunction. Japanese patent application Kokoku No. 6-3750 proposed a modular jack equipped with a mechanism to prevent plugging any plug having a different pole number.
FIGS. 14-18 show an eight-pole modular jack 1 as disclosed in the above Japanese patent specification. This eight-pole modular jack 1 receives such an eight-pole modular plug 2 as shown in FIG. 19.
In FIGS. 14 and 15, the modular jack 1 comprises a housing 3, eight terminals 4 arranged side by side within the housing 3, and a foolproof mechanism 5 provided in the top of the housing 3. A plug cavity 6 extends rearwardly from the front face of the housing 3 and has a central section 7 that is higher than side sections 8. A slot 10 is provided in a top wall 9 and has a trunk section 11 extending along the central section 7 of the plug cavity 6 and a pair of branch sections 12 extending outwardly from the front portion of said trunk section 11. Also, it has a pair of guiding slots 13 extending downwardly from the top of the housing 3 above the side sections 8 of the plug cavity 6.
In FIGS. 16-18, the foolproof mechanism 5 is cantilevered by the housing 3 at a rear portion 14 thereof and comprises a leaf spring 15 fitted in the trunk section 11 for vertical movement and a stopper-equipped cam member 17 fixed to the front portion of the leaf spring 15 fitted in the branch sections 12 for vertical movement. The stopper-equipped cam member 17 has a traverse arm section 18 with the central portion fixed to the front portion 16 of the leaf spring 15, a pair of stopper sections 19 extending downwardly from opposite ends of the arm section 18, and a pair of cam sections 20 provided on the outside of each stopper section 19. The leaf spring 15 is vertically flexible in the slot 10 so that the stopper-equipped cam member 17 is vertically movable along the guiding slots 13 with the rear portion 14 as a fulcrum. Each cam section 20 has a front portion 21 projecting forwardly beyond the stopper section 19 and a tapered face 22 extending rearwardly from the front portion 21. The outside width W1 (FIG. 17) of the cam sections 20 is substantially equal to the width of the eight-pole modular plug 2 and the inside width W2 of the cam sections 20 is made slightly larger than the six-pole modular plug 2′ in FIG. 20.
As shown in FIG. 19, the modular plug 2 has eight terminals 24 and a lock member 25 extending rearwardly from the front end. A pair of front ends 23 and a pair of vertical faces 26 are provided on opposite sides of the lock member 25.
When the eight-pole modular plug 2 is inserted into the eight-pole modular jack 1, the upper edges 27 of the front ends 23 abut and slide on the tapered faces 22 of the cam sections 20 while exerting upward forces on the cam sections 20. Consequently, the leaf spring 15 is flexed upwardly and the stopper-equipped cam member 17 is pushed up along the guiding slots 13 so that the eight-pole modular plug 2 can be inserted in the eight-pole modular jack 1.
As shown in FIG. 20, the modular plug 2′ has six terminals 24′ and a lock member 25′ extending rearwardly from the front end. A pair of front ends 23′ and a pair of vertical faces 26′ are provided on opposite sides of the lock member 25′.
When the six-pole modular plug 2′ is inserted into the eight-pole modular jack 1, the vertical faces 26′ of the modular plug 2′ abut against the front faces 28 of the stopper sections 19 to prevent further insertion of the modular plug 2′. Accordingly, the six-pole modular plug 2′ cannot be inserted into the eight-pole modular jack 1.
However, the leaf spring 15 is provided above the central section 7 of the plug cavity 6 and the stopper sections 19 extend downwardly from the arm section 18 so it is difficult to reduce the height of the modular jack 1. The leaf spring 15 and the stopper-equipped cam member 17 are separate components, keeping the number of components and the manufacturing cost high. The foolproof mechanism 5 is fitted in the slot 10 for vertical movement and the leaf spring 15 is flexible so that an accidental force can break the leaf spring.